U.S. patent application number 16/495949 was filed with the patent office on 2020-03-26 for heat treatment method for additive manufactured ni-base alloy object, method for manufacturing additive manufactured ni-base all.
This patent application is currently assigned to MITSUBISHI HEAVY INDUSTRIES, LTD.. The applicant listed for this patent is MITSUBISHI HEAVY INDUSTRIES, LTD.. Invention is credited to Kosuke FUJIWARA, Hidetaka HARAGUCHI, Nobuhiko SAITO, Masaki TANEIKE, Shuji TANIGAWA.
Application Number | 20200094325 16/495949 |
Document ID | / |
Family ID | 63675801 |
Filed Date | 2020-03-26 |
United States Patent
Application |
20200094325 |
Kind Code |
A1 |
TANEIKE; Masaki ; et
al. |
March 26, 2020 |
HEAT TREATMENT METHOD FOR ADDITIVE MANUFACTURED Ni-BASE ALLOY
OBJECT, METHOD FOR MANUFACTURING ADDITIVE MANUFACTURED Ni-BASE
ALLOY OBJECT, Ni-BASE ALLOY POWDER FOR ADDITIVE MANUFACTURED
OBJECT, AND ADDITIVE MANUFACTURED Ni-BASE ALLOY OBJECT
Abstract
A heat treatment method for an additive manufactured object
formed of a laminate-molded Ni-base alloy includes: a heat
treatment step for carbide precipitation optimization of heating
the additive manufactured object for 1 hour or longer and 100 hours
or shorter at a temperature which is equal to or higher than a
temperature T1 determined by Formula (1) according to amounts of
component elements and is equal to or lower than 1,350.degree. C.;
and an aging treatment step of heating the additive manufactured
object for 1 to 30 hours at a temperature of 800.degree. C. to
950.degree. C. after the heat treatment step for carbide
precipitation optimization. T1 (.degree. C.)=177.times.Ni
(%)+176.times.Co (%)+172.times.Cr (%)+178.times.Mo (%)+174.times.W
(%)+171.times.Al (%)+170.times.Ti (%)+168.times.Ta (%)+163.times.Nb
(%)+307.times.C (%)-16259 (1)
Inventors: |
TANEIKE; Masaki; (Tokyo,
JP) ; FUJIWARA; Kosuke; (Tokyo, JP) ;
HARAGUCHI; Hidetaka; (Tokyo, JP) ; TANIGAWA;
Shuji; (Tokyo, JP) ; SAITO; Nobuhiko; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUBISHI HEAVY INDUSTRIES, LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
MITSUBISHI HEAVY INDUSTRIES,
LTD.
Tokyo
JP
|
Family ID: |
63675801 |
Appl. No.: |
16/495949 |
Filed: |
March 26, 2018 |
PCT Filed: |
March 26, 2018 |
PCT NO: |
PCT/JP2018/011982 |
371 Date: |
September 20, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B33Y 10/00 20141201;
B22F 3/15 20130101; C22C 1/0433 20130101; B33Y 70/00 20141201; B22F
3/1055 20130101; B22F 3/1017 20130101; Y02P 10/25 20151101; B22F
2003/248 20130101; B33Y 80/00 20141201; B22F 2301/15 20130101; C22F
1/10 20130101; B22F 2998/10 20130101; C22C 19/051 20130101; B22F
3/24 20130101; B22F 2998/10 20130101; B22F 3/1055 20130101; B22F
2003/248 20130101; C22F 1/10 20130101; B22F 3/15 20130101; B22F
2003/248 20130101 |
International
Class: |
B22F 3/24 20060101
B22F003/24; C22C 19/05 20060101 C22C019/05; C22C 1/04 20060101
C22C001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 29, 2017 |
JP |
2017-064847 |
Claims
1-15. (canceled)
16. A heat treatment method for an additive manufactured Ni-base
alloy object which is performed on an additive manufactured object
formed of a Ni-base alloy laminate-molded into a predetermined
shape, the method comprising: a heat treatment step for carbide
precipitation optimization of heating the additive manufactured
object for 0.5 hours or longer and 100 hours or shorter at a
temperature which is equal to or higher than 1,255.degree. C.
according to contents (mass %) of component elements of the Ni-base
alloy and is equal to or lower than 1,350.degree. C.; and an aging
heat treatment step of heating the additive manufactured object for
1 to 30 hours at a temperature of 800.degree. C. to 950.degree. C.
after the heat treatment step for carbide precipitation
optimization, wherein the Ni-base alloy contains, by mass %, Co:
15% to 25%, Cr: 10% to 25%, Mo: 0% to 3.5%, W: 0.5% to 10%, Al:
1.0% to 4.0%, Ti: 0% to 5.0%, Ta: 0% to 4.0%, Nb: 0% to 2.0%, C:
0.03% to 0.2%, B: 0.001% to 0.02%, Zr: 0% to 0.1%, and a balance
consisting of Ni and unavoidable impurities.
17. The heat treatment method for an additive manufactured Ni-base
alloy object according to claim 16, wherein the Ni-base alloy
contains, by mass %, Al (%)+0.5.times.Ti (%) is 1% to 5%, and W
(%)+0.5.times.Mo (%) is 0.5% to 10%.
18. The heat treatment method for an additive manufactured Ni-base
alloy object according to claim 16, in the heat treatment step for
carbide precipitation optimization, a lower limit temperature T1 is
determined by Formula (1): T1 (.degree. C.)=177.times.Ni
(%)+176.times.Co (%)+172.times.Cr (%)+178.times.Mo (%)+174.times.W
(%)+171.times.Al (%)+170.times.Ti (%)+168.times.Ta (%)+163.times.Nb
(%)+307.times.C (%)-16259 (1).
19. The heat treatment method for an additive manufactured Ni-base
alloy object according to claim 16, wherein a total content of Ti,
Ta, and Nb in the Ni-base alloy is 10.0% or less by mass %.
20. The heat treatment method for an additive manufactured Ni-base
alloy object according to claim 16, further comprising: a solution
heat treatment step of heating the additive manufactured object for
0.5 to 10 hours at a temperature of 1,150.degree. C. to
1,250.degree. C. between the heat treatment step for carbide
precipitation optimization and the aging heat treatment step.
21. The heat treatment method for an additive manufactured Ni-base
alloy object according to claim 16, wherein a heat treatment for
stress removal is performed on the additive manufactured object
before the heat treatment step for carbide precipitation
optimization.
22. The heat treatment method for an additive manufactured Ni-base
alloy object according to claim 16, wherein a HIP treatment is
performed on the additive manufactured object after the heat
treatment step for carbide precipitation optimization and before
the aging heat treatment step.
23. The heat treatment method for an additive manufactured Ni-base
alloy object according to claim 16, wherein a stabilization heat
treatment is performed after the heat treatment step for carbide
precipitation optimization and before the aging heat treatment
step.
24. A heat treatment method for an additive manufactured Ni-base
alloy object, wherein one or more M.sub.23C.sub.6 carbides are
precipitated on average at grain boundaries per 10 .mu.m of grain
boundary length by the heat treatment method for an additive
manufactured Ni-base alloy object according to claim 16.
25. A method for manufacturing an additive manufactured Ni-base
alloy object, the method comprising: an additive manufacturing step
of forming an additive manufactured object formed of a Ni-base
alloy on a substrate by repeating a process of melting a Ni-base
alloy powder and forming a rapidly solidified layer on the
substrate; and subsequently subjecting the additive manufactured
object to the heat treatment method for an additive manufactured
Ni-base alloy object according to claim 16.
26. A Ni-base alloy powder for an additive manufactured object
comprising, by mass %: Co: 17% to 22%; Cr: 15% to 22%; Mo: 0% to
2%; W: 4% to 8%; Al: 1.5% to 3.5%; Ti: 1.0% to 4.0%; Ta: 0% to
3.0%; Nb: 0% to 1.5%; C: 0.06% to 0.15%; B: 0.001% to 0.01%; Zr: 0%
to 0.04%, and a balance consisting of Ni and unavoidable
impurities.
27. The Ni-base alloy powder for an additive manufactured object
according to claim 26, wherein the Ni-base alloy powder contains,
by mass %: Al (%)+0.5.times.Ti (%) is 1% to 5%, W (%)+0.5.times.Mo
(%) is 0.5% to 10%.
28. The Ni-base alloy powder for an additive manufactured object
according to claim 26, wherein an average grain size is 100 .mu.m
or less.
29. The Ni-base alloy powder for an additive manufactured object
according to claim 26, wherein the Ni-base alloy powder contains,
by mass %, one or both of Ta: 0.01% to 3.0% and Nb: 0.01% to
1.5%.
30. The Ni-base alloy powder for an additive manufactured object
according to claim 26, wherein the average grain size is 10 .mu.m
to 45 .mu.m.
31. An additive manufactured Ni-base alloy object comprising: the
Ni-base alloy having the composition according to claim 26, wherein
one or more M.sub.23C.sub.6 carbides are precipitated on average at
grain boundaries per 10 .mu.m of grain boundary length.
Description
TECHNICAL FIELD
[0001] The present invention relates to a heat treatment method for
an additive manufactured Ni-base alloy object, a method for
manufacturing an additive manufactured Ni-base alloy object, a
Ni-base alloy powder for an additive manufactured object, and an
additive manufactured Ni-base alloy object.
[0002] Priority is claimed on Japanese Patent Application No.
2017-064847, filed on Mar. 29, 2017, the content of which is
incorporated herein by reference.
BACKGROUND ART
[0003] In recent years, metal additive manufacturing techniques
have been developed and put to practical use among so-called 3D
printer (three-dimensional modeling) technologies. In this type of
metal additive manufacturing method, a metal powder layer that
serves as a raw material of a metallic shaped object that becomes a
product is disposed on a base plate, and a predetermined region on
the metal powder layer is irradiated with high-density energy such
as a laser. Then, the metal powder in the region is rapidly melted,
rapidly cooled, and solidified to form a metal solidified layer
having a predetermined shape. By repeating such a process, a
three-dimensionally shaped laminate is formed.
[0004] Ni-base alloys containing Ni as a main component have been
known to have high heat resisting properties and a high
high-temperature strength, and members made of a Ni-base alloy
through a casting method have been widely used for heat resisting
members such as turbine members for a gas turbine which require a
high-temperature strength.
[0005] Attempts have recently been made to apply a metal additive
manufacturing method capable of performing shaping in series
without complicated manufacturing steps as a method for
manufacturing a component made of a Ni-base alloy with a
complicated shape such as a component having an internal cooling
passage (for example, PTL 1).
CITATION LIST
Patent Literature
[0006] [PTL 1] Japanese Patent No. 5840593
DISCLOSURE OF INVENTION
Technical Problem
[0007] Even in a case where a heat resisting member made of a
Ni-base alloy is manufactured by a metal additive manufacturing
method, a long high temperature creep life is preferable.
[0008] Particularly, turbine components and the like which are
actually used have complicated shapes and many irregularities or
notch parts in their surfaces, and thus the members do not always
have smooth surfaces in many cases. In that case, it is desirable
for members with complicated shapes or members with many
irregularities which are actually used to have a long high
temperature creep life (notch high temperature creep life) in a
high temperature creep rupture test which is performed using a
notch test piece.
[0009] The invention has been contrived in view of the above
circumstances, and an object of the invention is to provide a heat
treatment method for obtaining an additive manufactured Ni-base
object, which is capable of improving a notch high temperature
creep life, a method for manufacturing an additive manufactured
Ni-base alloy object, a Ni-base alloy powder for an additive
manufactured object, and an additive manufactured Ni-base alloy
object.
Solution to Problem
[0010] The inventors of the invention have repeatedly conducted
intensive experiments and studies to find means for significantly
extending the notch high temperature creep life by causing notch
strengthening in a heat resisting Ni-base alloy member obtained by
an additive manufacturing method, and found that in a case where a
heat treatment is appropriately performed on the additive
manufactured object according to a composition of the Ni-base
alloy, notch weakening is turned into notch strengthening, and thus
the notch high temperature creep life can be significantly
extended.
[0011] Specifically, according to a first aspect of the invention,
there is provided a heat treatment method for an additive
manufactured Ni-base alloy object which is performed on an additive
manufactured object formed of a Ni-base alloy laminate-molded into
a predetermined shape, having: a heat treatment step for carbide
precipitation optimization of heating the additive manufactured
object for 0.5 hours or longer and 100 hours or shorter at a
temperature which is equal to or higher than a temperature T1
determined by Formula (1) according to contents (mass %) of
component elements of the Ni-base alloy and is equal to or lower
than 1,350.degree. C.; and an aging heat treatment step of heating
the additive manufactured object for 1 to 30 hours at a temperature
of 800.degree. C. to 950.degree. C. after the heat treatment step
for carbide precipitation optimization.
T1 (.degree. C.)=177.times.Ni (%)+176.times.Co (%)+172.times.Cr
(%)+178.times.Mo (%)+174.times.W (%)+171.times.Al (%)+170.times.Ti
(%)+168.times.Ta (%)+163.times.Nb (%)+307.times.C (%)-16259 (1)
[0012] According to a second aspect of the invention, in the heat
treatment method for an additive manufactured Ni-base alloy object
of the first aspect, the Ni-base alloy contains, by mass %, Co: 15%
to 25%, Cr: 10% to 25%, Mo: 0% to 3.5%, W: 0.5% to 10%, Al: 1.0% to
4.0%, Ti: 0% to 5.0%, Ta: 0% to 4.0%, Nb: 0% to 2.0%, C: 0.03% to
0.2%, B: 0.001% to 0.02%, Zr: 0% to 0.1%, and a balance consisting
of Ni and unavoidable impurities, Al (%)+0.5.times.Ti (%) is 1% to
5%, and W (%)+0.5.times.Mo (%) is 0.5% to 10%.
[0013] According to a third aspect of the invention, in the heat
treatment method for an additive manufactured Ni-base alloy object
of the second aspect, a total content of Ti, Ta, and Nb in the
Ni-base alloy is 10.0% or less by mass %.
[0014] According to a fourth aspect of the invention, the heat
treatment method for an additive manufactured Ni-base alloy object
of any one of the first to third aspects further includes a
solution heat treatment step of heating the additive manufactured
object for 0.5 to 10 hours at a temperature of 1,150.degree. C. to
1,250.degree. C. between the heat treatment step for carbide
precipitation optimization and the aging heat treatment step.
[0015] According to a fifth aspect of the invention, in the heat
treatment method for an additive manufactured Ni-base alloy object
of any one of the first to fourth aspects, a heat treatment for
stress removal is performed on the additive manufactured object
before the heat treatment step for carbide precipitation
optimization.
[0016] According to a sixth aspect of the invention, in the heat
treatment method for an additive manufactured Ni-base alloy object
of any one of the first to fifth aspects, a HIP treatment is
performed on the additive manufactured object after the heat
treatment step for carbide precipitation optimization and before
the aging heat treatment step.
[0017] According to a seventh aspect of the invention, in the heat
treatment method for an additive manufactured Ni-base alloy object
of any one of the first to sixth aspects, a stabilization heat
treatment is performed after the heat treatment step for carbide
precipitation optimization and before the aging heat treatment
step.
[0018] According to an eighth aspect of the invention, there is
provided a heat treatment method for an additive manufactured
Ni-base alloy object, in which one or more M.sub.23C.sub.6 carbides
are precipitated on average at grain boundaries per 10 .mu.m of
grain boundary length by the heat treatment method for an additive
manufactured Ni-base alloy object according to any one of the first
to seventh aspects.
[0019] According to a ninth aspect of the invention, there is
provided a method for manufacturing an additive manufactured
Ni-base alloy object, having: an additive manufacturing step of
forming an additive manufactured object formed of a Ni-base alloy
on a substrate by repeating a process of melting a Ni-base alloy
powder and forming a rapidly solidified layer on the substrate; and
subsequently subjecting the additive manufactured object to the
heat treatment method for an additive manufactured Ni-base alloy
object according to any one of the first to seventh aspects.
[0020] According to a tenth aspect of the invention, in the method
for manufacturing an additive manufactured Ni-base alloy object of
the ninth aspect, an additive manufactured Ni-base alloy object in
which one or more M.sub.23C.sub.6 carbides are precipitated on
average at grain boundaries per 10 .mu.m of grain boundary length
is obtained.
[0021] According to an eleventh aspect of the invention, there is
provided a Ni-base alloy powder for an additive manufactured object
containing, by mass %: Co: 15% to 25%; Cr: 10% to 25%; Mo: 0% to
3.5%; W: 0.5% to 10%; Al: 1.0% to 4.0%; Ti: 0% to 5.0%; Ta: 0% to
4.0%; Nb: 0% to 2.0%; C: 0.03% to 0.2%; B: 0.001% to 0.02%; Zr: 0%
to 0.1%; and a balance consisting of Ni and unavoidable impurities,
in which Al (%)+0.5.times.Ti (%) is 1% to 5%, W (%)+0.5.times.Mo
(%) is 0.5% to 10%, and an average grain size is 100 .mu.m or
less.
[0022] According to a twelfth aspect of the invention, the Ni-base
alloy powder for an additive manufactured object of the eleventh
aspect contains, by mass %: Co: 17% to 22%; Cr: 15% to 22%; Mo: 0%
to 2%; W: 4% to 8%; Al: 1.5% to 3.5%; Ti: 1.0% to 4.0%; Ta: 0% to
3.0%; Nb: 0% to 1.5%; C: 0.06% to 0.15%; B: 0.001% to 0.01%; and
Zr: 0% to 0.04%.
[0023] According to a thirteenth aspect of the invention, the
Ni-base alloy powder for an additive manufactured object of the
eleventh or twelfth aspect contains, by mass %, one or both of Ta:
0.01% to 3.0% and Nb: 0.01% to 1.5%.
[0024] According to a fourteenth aspect of the invention, in the
Ni-base alloy powder for an additive manufactured object of any one
of the eleventh to thirteenth aspects, the average grain size is 10
.mu.m to 45 .mu.m.
[0025] According to a fifteenth aspect of the invention, there is
provided an additive manufactured Ni-base alloy object including:
the Ni-base alloy having the composition according to any one of
the eleventh to thirteenth aspects, in which one or more
M.sub.23C.sub.6 carbides are precipitated on average at grain
boundaries per 10 .mu.m of grain boundary length.
Advantageous Effects of Invention
[0026] According to a heat treatment method for obtaining an
additive manufactured Ni-base object, a method for manufacturing an
additive manufactured Ni-base alloy object, a Ni-base alloy powder
for an additive manufactured object, and an additive manufactured
Ni-base alloy object of the invention, it is possible to improve a
notch high temperature creep life.
BRIEF DESCRIPTION OF DRAWINGS
[0027] FIG. 1 is a graph showing a relationship between an average
number of M.sub.23C.sub.6 carbides per 10 .mu.m of grain boundary
length in an additive manufactured Ni-base object and a creep life
ratio obtained by a high temperature creep test at 760.degree.
C.
[0028] FIG. 2 is a graph showing a relationship between a
temperature of a heat treatment for carbide precipitation
optimization for the additive manufactured Ni-base object and a
creep life ratio obtained by a high temperature creep test at
760.degree. C.
[0029] FIG. 3 is a metallographic cross-sectional structure
photograph of the additive manufactured Ni-base object after an
aging heat treatment in a case where a heat treatment for carbide
precipitation optimization is not performed.
[0030] FIG. 4 is a metallographic cross-sectional structure
photograph of the additive manufactured Ni-base object after the
aging heat treatment in a case where the heat treatment for carbide
precipitation optimization is performed.
[0031] FIG. 5 is a flowchart showing an example of a method for
manufacturing an additive manufactured object as an aspect of the
invention, including an example of a heat treatment method.
[0032] FIG. 6 is a plan view showing a notch test piece for a high
temperature creep rupture test.
[0033] FIG. 7 is an enlarged cross-sectional view of a major part,
showing a notch part of the notch test piece shown in FIG. 6.
[0034] FIG. 8 is a plan view showing a smooth test piece for a high
temperature creep rupture test.
BEST MODE FOR CARRYING OUT THE INVENTION
[0035] Hereinafter, embodiments of a heat treatment method for an
additive manufactured Ni-base alloy object, a method for
manufacturing an additive manufactured Ni-base alloy object, a
Ni-base alloy powder for an additive manufactured object, and an
additive manufactured Ni-base alloy object according to the
invention will be described in detail.
[0036] <Experiments and Findings>
[0037] First, experiments performed by the inventors of the
invention and findings obtained from the tests will be
described.
[0038] In a heat resisting Ni-base alloy, a high-temperature
strength is exhibited by a precipitation strengthening effect due
to the precipitation of an intermetallic compound phase called a
.gamma.' phase However, in a case where the heat resisting Ni-base
alloy is solidified or heat-treated, not only such intermetallic
compounds but also carbides precipitate. The characteristics after
a final heat treatment change with the precipitation form of the
carbides.
[0039] Regarding the carbides in this type of Ni-base alloy,
various different types of carbides precipitate depending on the
type and amount of alloying elements, and representative carbides
are M.sub.23C.sub.6 carbides and MC carbides, where M represents a
metal element and C represents carbon.
[0040] Regarding a material (cast material) formed of a Ni-base
alloy obtained by a conventional general casting method and a
material (additive manufactured material) formed of a Ni-base alloy
obtained by an additive manufacturing method, a metallographic
structure before a heat treatment and a precipitation situation of
carbides have been examined, and it has been confirmed that a
solidification rate after melting of the powder with a laser or the
like is much higher than a solidification rate in a case where the
molten metal is solidified by the general casting method, and thus
the crystal structure of the additive manufactured material is much
finer than that of the cast material, and the grain size of the
additive manufactured material is about several tens of .mu.m while
the grain size of the cast material is on the order of mm. In
addition, in the cast material, coarse MC carbides are scattered
around grain boundaries, and a certain level of grain boundary
strength is obtained by M.sub.23C.sub.6 carbides precipitating at
the grain boundaries by a subsequent heat treatment. In the
additive manufactured material, solidification is performed much
more rapidly than in the cast material, and thus MC carbides finely
precipitate throughout the material including the inside of the
crystal grains during solidification. Since the MC carbides are
stable even at high temperatures, they are not solid-solubilized
even after being heat-treated under the same conditions as in the
case of the case material, and thus the MC carbides are finely
dispersed and precipitated also inside the crystal grains. In a
case where the MC carbides are not solid-solubilized as described
above, the M.sub.23C.sub.6 carbides undergoing a subsequent
solution treatment and an aging heat treatment are not sufficiently
precipitated (mainly, precipitation at the grain boundaries), and
thus they are combined and a sufficient grain boundary strength is
not obtained. As a result, it has been found that high temperature
creep characteristics of the additive manufactured material are
inferior to those of the cast material, and particularly, a
reduction in the notch high temperature creep life, that is, notch
weakening, occurs.
[0041] Based on such recognition, it has been thought that in a
case where a precipitation situation of carbides in the additive
manufactured material, particularly, a precipitation situation of
carbides by the heat treatment, is appropriately controlled, the
grain boundaries of the additive manufactured material are
strengthened, and the high temperature creep characteristics can
thus be improved. As a result of various experiments and studies
which have been repeatedly conducted, it has been found that in
order to provide a material exhibiting notch strengthening by
strengthening the grain boundaries of the additive manufactured
material, one or more M.sub.23C.sub.6 carbides are necessary to be
present on average at the grain boundaries per 10 .mu.m of grain
boundary length.
[0042] That is, in a case where a high temperature creep life
(notch high temperature creep life) obtained using a notch test
piece (notched test piece) in a high temperature creep rupture test
is longer than a high temperature creep life (smooth high
temperature creep life) obtained in a case where a smooth test
piece having no notch is subjected to the high temperature creep
rupture test, the high temperature creep characteristics,
particularly, the high temperature notch creep characteristics, can
be determined to be good (that is, a notch strengthening state),
and thus in a case where a ratio of "notch high temperature creep
life" divided by "smooth high temperature creep life" is defined as
a creep life ratio, and the creep life ratio exceeds 1, it can be
judged that notch strengthening characteristics are exhibited, and
good high temperature creep characteristics, particularly,
excellent notch high temperature creep characteristics, are
obtained.
[0043] Accordingly, a heat treatment for carbide precipitation
optimization is performed on the additive manufactured Ni-base
alloy object before the solution heat treatment-aging heat
treatment for precipitation of a .gamma.' phase, and heat treatment
conditions for the heat treatment for carbide precipitation
optimization are variously changed to examine a relationship
between a precipitation situation of intergranular precipitates
mainly containing M.sub.23C.sub.6 carbides after the final solution
heat treatment-aging heat treatment, particularly, the number of
M.sub.23C.sub.6 carbides precipitated per unit grain boundary
length at the grain boundaries and a creep life ratio obtained by a
high temperature creep test at 760.degree. C. As a result, as shown
in FIG. 1, it has been found that in a case where the number of
M.sub.23C.sub.6 carbides precipitated per unit grain boundary
length is increased, the creep life ratio is increased, and
particularly, in a case where the number of intergranular carbides
formed of M.sub.23C.sub.6 carbides per 10 .mu.m of grain boundary
length is one or more on average, the creep life ratio exceeds
1.
[0044] It has further been found that in the above-described
experiment, by appropriately setting the conditions for the heat
treatment for carbide precipitation optimization before the
additive manufactured Ni-base alloy object is subjected to the
solution heat treatment-aging heat treatment for formation of a
.gamma.' phase, the precipitation situation (precipitation
situation at the grain boundaries) of the M.sub.23C.sub.6 carbides
is optimized, one or more M.sub.23C.sub.6 carbides are precipitated
on average per 10 .mu.m of grain boundary length, and thus a creep
life ratio exceeding 1 can be secured. That is, the inventors of
the invention have conducted a heat treatment for carbide
precipitation optimization at various temperatures, and then
performed a solution heat treatment and an aging heat treatment in
the same manner as in a case of a conventional cast material to
examine a relationship between the temperature of the heat
treatment for carbide precipitation optimization and the creep life
ratio, and found that, as shown in FIG. 2, in a case where the
temperature of the heat treatment for carbide precipitation
optimization is increased, the creep life ratio is increased, and
particularly, in a case where the temperature of the heat treatment
for carbide precipitation optimization is higher than a temperature
T1 that is determined by Formula (1) according to a composition of
the Ni-base alloy, the creep life ratio is rapidly increased, and a
creep life ratio exceeding 1 can be secured. The temperature T1 of
the Ni-base alloy used in the experiment, that is determined by
Formula (1), is 1,255.degree. C.
T1 (.degree. C.)=177.times.Ni (%)+176.times.Co (%)+172.times.Cr
(%)+178.times.Mo (%)+174.times.W (%)+171.times.Al (%)+170.times.Ti
(%)+168.times.Ta (%)+163.times.Nb (%)+307.times.C (%)-16259 (1)
[0045] Hereinafter, embodiments of a heat treatment method for an
additive manufactured Ni-base alloy object, a method for
manufacturing an additive manufactured Ni-base alloy object, a
Ni-base alloy powder for an additive manufactured object, and an
additive manufactured Ni-base alloy object according to the
invention will be described in detail.
[0046] <Carbides in Additive Manufactured Object>
[0047] In a Ni-base alloy, M.sub.23C.sub.6 carbides and MC carbides
mainly precipitate as described above.
[0048] In these carbides, M in the M.sub.23C.sub.6 carbide is
mainly formed of Cr, Ni, and W. Such M.sub.23C.sub.6 carbides
precipitate at grain boundaries by being subjected to a solution
heat treatment and an aging heat treatment after formation of an
additive manufactured object (after rapid solidification of the
Ni-base alloy powder), and increase a grain boundary strength,
thereby suppressing intergranular fracture during creep
deformation, and exhibiting notch strengthening characteristics by
an increase in the resistance to stress concentration. That is, a
notch high temperature creep life is increased, and this
contributes to an increase in the high temperature creep life ratio
("notch high temperature creep life" divided by "smooth high
temperature creep life").
[0049] M in the MC carbides is mainly formed of Ti, Ta, and Nb.
Such MC carbides precipitate during rapid solidification of the
Ni-base alloy powder for additive manufacturing. As described
above, the MC carbides sparsely precipitate as coarse precipitates
during solidification in a conventional cast material including
grain boundaries, but in an additive manufactured object, the MC
carbides finely precipitate inside the crystal grains by melting
and rapid solidification of the Ni-base alloy powder. In a case
where the amount of MC carbides precipitating during the rapid
solidification is too large in the additive manufactured object, a
large amount of carbon is fixed, the amount of M.sub.23C.sub.6
carbides precipitating in the subsequent aging heat treatment is
reduced, and as a result, the grain boundaries are not sufficiently
strengthened.
[0050] Here, in order to reduce the amount of MC carbides
precipitating during the rapid solidification, it is effective to
reduce the amount of Ti, Ta, and Nb to be added, which are
constituent elements of the MC carbides. However, since Ti, Ta, and
Nb are also constituent elements of the .gamma.' phase as a
strengthening phase of the matrix, the above elements are
necessarily added in a certain amount. Accordingly, in this
embodiment, an appropriate heat treatment (heat treatment for
carbide precipitation optimization) is performed before the
solution heat treatment to decompose the MC carbides precipitating
during the rapid solidification and to thus solid-solubilize carbon
(C) in the matrix. By performing the heat treatment for carbide
precipitation optimization as described above, the amount of
M.sub.26C.sub.6 carbides precipitating at the grain boundaries due
to a subsequent aging heat treatment is sufficiently secured.
[0051] FIG. 3 shows a cross-sectional structure in the additive
manufactured Ni-base alloy object in a case where the
above-described heat treatment for carbide precipitation
optimization is not performed. In this case, the MC carbides are
finely dispersed and precipitated throughout the inside of the
grains and the grain boundaries. The number of M.sub.23C.sub.6
carbides precipitated is small.
[0052] FIG. 4 shows a cross-sectional structure in the additive
manufactured Ni-base alloy object in a case where the heat
treatment for carbide precipitation optimization is performed under
appropriate conditions. In this case, it is found that
M.sub.23C.sub.6 carbides precipitate at the grain boundaries, and
MC carbides precipitate to some extent inside the grains.
[0053] In the additive manufactured Ni-base alloy object as an
embodiment of the invention, one or more M.sub.23C.sub.6 carbides
necessarily precipitate per 10 .mu.m of grain boundary length as a
condition for precipitation of M.sub.23C.sub.6 carbides after the
aging heat treatment. Here, in a case where the number of
M.sub.23C.sub.6 carbides precipitating per 10 .mu.m of grain
boundary length is less than 1, the grain boundaries are not
sufficiently strengthened, and thus it is difficult to secure a
high temperature creep life ratio exceeding 1 as described with
reference to FIG. 1. In other words, it is difficult to exhibit
notch strengthening characteristics.
[0054] <Composition of Ni-Base Alloy Powder>
[0055] In the embodiment of the invention, the composition of a
Ni-base alloy powder for an additive manufactured object is
determined from the viewpoint of securing a sufficient amount of
M.sub.23C.sub.6 carbides precipitating due to an appropriate heat
treatment for carbide precipitation optimization while securing the
amount of the .gamma.' phase precipitating as a strengthening phase
of the matrix.
[0056] That is, basically, the Ni-base alloy powder for an additive
manufactured object according to this embodiment contains, by mass
%, Co: 15% to 25%, Cr: 10% to 25%, W: 0.5% to 10%, Al: 1.0% to
4.0%, Ti: 0% to 5.0%, Ta: 0% to 4.0%, Nb: 0% to 2.0%, C: 0.03% to
0.2%, B: 0.001% to 0.02%, Zr: 0% to 0.1%, and a balance consisting
of Ni and unavoidable impurities, Al (%)+0.5.times.Ti (%) is within
a range of 1% to 5%, and W (%)+0.5.times.Mo (%) is within a range
of 0.5% to 10%.
[0057] In the Ni-base alloy powder for an additive manufactured
object according to this embodiment, a total content of Ti, Ta, and
Nb among the above components is preferably 10.0% or less.
[0058] In this embodiment, the reasons for limiting the composition
of the Ni-base alloy powder are as follows.
[0059] [Co: 15% to 25%]
[0060] Co has an effect of increasing the limit (solid solution
limit) of solid-solubilization of Ti, Al, and the like in the
matrix at high temperatures. Accordingly, it not only acts to
finely disperse and precipitate the .gamma.' phase (compounds such
as Ni, Ti, Al, and Ta) by a solution heat treatment-aging heat
treatment, thereby improving the strength of the matrix, but also
has an effect of promoting the solid-solubilization of MC carbides
during a heat treatment for carbide precipitation optimization.
Particularly, in order to obtain the latter of the above effects,
15% or greater of Co is needed. In a case where the Co content is
greater than 25%, a harmful phase precipitates and embrittles, and
a high-temperature strength decreases. Accordingly, the Co content
is within a range of 15% to 22%. It is particularly desirable for
the Co content to be within a range of 17% to 22%.
[0061] [Cr: 10% to 25%]
[0062] Cr is an element effective for improving the oxidation
resistance at high temperatures. However, in a case where the
content thereof is less than 10%, an improvement in the
high-temperature oxidation resistance by addition of Cr is not
sufficiently exhibited. Cr is a constituent element of a
M.sub.23C.sub.6 carbide. In a case where the Cr amount is less than
10%, the amount of M.sub.23C.sub.6 carbides to be precipitated is
reduced, and it becomes difficult to extend the high temperature
creep life. It is not preferable for the Cr amount to be greater
than 25% since a harmful phase precipitates, and thus the strength
and the ductility are reduced. Accordingly, the Cr content is
within a range of 10% to 25%. It is desirable for the Cr content to
be within a range of 15% to 22% in the above range.
[0063] [W: 0.5% to 10%]
[0064] W is solid-solubilized into a .gamma. phase as a matrix and
has an effect of improving a strength by solid solution
strengthening. W is a constituent element of a M.sub.23C.sub.6
carbide. However, since it is an element which slowly diffuses, it
has an effect of suppressing the coarsening of the M.sub.23C.sub.6
carbide. In order to exhibit these effects, it is necessary to add
0.5% or greater of W. However, in a case where the W amount is
greater than 10%, a harmful phase precipitates, and thus the
strength and the ductility are reduced. Accordingly, the W content
is within a range of 0.5% to 10%. It is particularly desirable for
the W content to be within a range of 4% to 8% in the above
range.
[0065] [Al: 1.0% to 4.0%]
[0066] Al is an element which generates a .gamma.' phase, and has
an effect of improving oxidation resistance and corrosion
resistance at high temperature while increasing a high-temperature
strength of the alloy, particularly, a high temperature creep
strength by precipitation strengthening by the .gamma.' phase
precipitation grains. In a case where the Al amount is less than
1.0%, the amount of the .gamma.' phase to be precipitated is
reduced, and thus precipitation strengthening by the precipitates
is not sufficiently achieved. In a case where the Al amount is
greater than 4.0%, the weldability is reduced, and cracking
frequently occurs during additive manufacturing. Accordingly, the
Al content is within a range of 1.0% to 4.0%. Particularly, it is
desirable for the Al content to be within a range of 1.5% to 3.5%
in the above range.
[0067] [C: 0.03% to 0.2%]
[0068] C generates carbides represented by M.sub.23C.sub.6 carbides
and MC carbides, and particularly, precipitates M.sub.23C.sub.6
carbides at grain boundaries by an appropriate heat treatment to
provide grain boundary strengthening and notch strengthening. In a
case where the C content is less than 0.03%, the amount of carbides
is too small, and no strengthening effect can be expected. In a
case where the C content is greater than 0.2%, the amount of MC
carbides precipitating inside the crystal grains is large and the
intragranular strength is too large compared to the grain boundary
strength, and thus notch weakening is exhibited. Accordingly, the C
content is within a range of 0.03% to 0.2%. It is particularly
desirable for the C content to be within a range of 0.06% to 0.15%
in the above range.
[0069] [B: 0.001% to 0.02%]
[0070] B strengthens the grain boundaries by being present at the
grain boundaries, and is effective in improving a high temperature
creep strength and notch weakening. In order to obtain these
effects, it is necessary to add 0.001% or greater of B. In a case
where the B amount is greater than 0.02%, there is a concern that a
boride may be generated and the ductility may be reduced.
Accordingly, the B content is within a range of 0.001% to 0.02%. It
is particularly desirable for the B content to be within a range of
0.001% to 0.01% in the above range.
[0071] [Ti: 0% to 5.0%]
[0072] Ti is an element which generates a .gamma.' phase, and has
an effect of improving oxidation resistance and corrosion
resistance at high temperature while increasing a high-temperature
strength of the alloy, particularly, a high temperature creep
strength by precipitation strengthening by the .gamma.' phase
precipitation grains. In a case where the Ti amount is greater than
5.0%, there is a concern that the weldability may be reduced, and
cracking may frequently occur during additive manufacturing.
Moreover, since the amount of MC carbides to be precipitated
increases, carbon is fixed, and thus even in a case where a heat
treatment for carbide precipitation optimization is performed, the
amount of M.sub.23C.sub.6 carbides as intergranular precipitates to
be precipitated is reduced. Accordingly, the Ti amount is required
to be suppressed to 5.0% or less. Accordingly, the amount of Ti to
be added is within a range of 0% to 5.0%. In a case where Ti is
added, the Ti amount is preferably 0.01% or greater, and more
preferably within a range of 1.0% to 4.0%.
[0073] [Al+0.5Ti: 1% to 5%]
[0074] In a case where Ti is added among Ti, Ta, and Nb, the amount
of "Al+0.5Ti" is within a range of 1% to 5%. In a case where the
amount of "Al+0.5Ti" is less than 1%, the amount of the .gamma.'
phase to be precipitated, which contributes to strengthening, is
reduced, and thus there is a concern that the strength may be
reduced. In a case where the amount of "Al+0.5Ti" is greater than
5.0%, the weldability is reduced, and cracking frequently occurs
during additive manufacturing.
[0075] [Ta: 0% to 4.0%]
[0076] Ta is also an element which generates a .gamma.' phase, and
increases a high-temperature strength of the alloy, particularly, a
high temperature creep strength by precipitation strengthening by
the .gamma.' phase precipitation grains. Ta is an element which
generates stable MC carbides inside the crystal grains at high
temperatures. In a case where 4.0% or greater of Ta is added,
carbon is fixed, and thus even in a case where a heat treatment for
carbide precipitation optimization is performed, M.sub.23C.sub.6 as
intergranular precipitates is not generated, and notch weakening is
exhibited. Accordingly, the amount of Ta is within a range of 0% to
4.0%. In a case where Ta is added, it is desirable for the Ta
amount to be within a range of 0.01% to 3.0%.
[0077] [Nb: 0% to 2.0%]
[0078] Nb is also an element which generates a .gamma.' phase, and
increases a high-temperature strength of the alloy, particularly, a
high temperature creep strength by precipitation strengthening by
the .gamma.' phase precipitation grains. Nb is an element which
generates stable MC carbides inside the crystal grains at high
temperatures. In a case where 2.0% or greater of Nb is added,
carbon is fixed, and thus even in a case where a heat treatment for
carbide precipitation optimization is performed, M.sub.23C.sub.6
carbides as intergranular precipitates are not generated.
Accordingly, the amount of Nb to be added is within a range of 0%
to 2.0%. In a case where Ta is added, it is desirable for the Ta
amount to be within a range of 0.01% to 1.5% in the above
range.
[0079] [Total Content of Ti, Ta, and Nb: 1.0% to 10.0%]
[0080] In a case where a total content of Ti, Ta, and Nb is less
than 1.0%, the effect of increasing a high-temperature strength of
the alloy, particularly, a high temperature creep strength by
precipitation strengthening by the .gamma.' phase precipitation
grains, is not sufficiently exhibited. In a case where the total
content of Ti, Ta, and Nb is greater than 10.0%, carbon is fixed,
and as a result, even in a case where a heat treatment for carbide
precipitation optimization is performed, there is a concern that
M.sub.23C.sub.6 as intergranular precipitates may not be generated,
and notch weakening may be exhibited. Accordingly, the total
content of Ti, Ta, and Nb is 1.0% to 10.0%. The total content of
Ti, Ta, and Nb is preferably within a range of 4.0% to 8.0% in the
above range.
[0081] [Mo: 0% to 3.5%]
[0082] As similar to W, Mo is solid-solubilized into a .gamma.
phase as a matrix and has an effect of improving a strength by
solid solution strengthening. In a case where the Mo amount is
greater than 3.5%, a harmful phase precipitates, and thus the
strength and the ductility are reduced. Accordingly, in a case
where Mo is added, the amount of Mo to be added is within a range
of 0% to 3.5%. In a case where Mo is added, it is particularly
desirable for the Mo amount to be within a range of 0.01% to 2% in
the above range.
[0083] [W+0.5Mo: 0.5% to 10%]
[0084] In a case where Mo is added together with W and the amount
of "W+0.5Mo" is greater than 10%, a harmful phase precipitates, and
thus the strength and the ductility are reduced. In a case where
the amount of "W+0.5Mo" is less than 0.5%, the effect of improving
the strength by solid solution strengthening by the addition of Mo
and W is not sufficiently obtained. Accordingly, in a case where Mo
is added together with W, the amount of "W+0.5Mo" is within a range
of 0.5% to 10%.
[0085] [Zr: 0% to 0.1%]
[0086] Zr strengthens the grain boundaries by being present at the
grain boundaries, and has an effect of improving a high temperature
creep strength and notch weakening. In a case where the Zr amount
is greater than 0.1%, there is a concern that the melting point of
the grain boundary part may be locally reduced, and the strength
may be reduced. Accordingly, the Zr amount is within a range of 0%
to 0.1%. In a case where Zr is added, it is desirable for the Zr
amount to be within a range of 0.01% to 0.04%.
[0087] The balance of the above elements consists of Ni and
unavoidable impurities. In this type of Ni-base alloy, Fe, Si, Mn,
Cu, P, S, N, and the like may be contained as unavoidable
impurities, and it is desirable for the amount of each of Fe, Si,
Mn, and Cu to be 0.5% or less, and for the amount of each of P, S,
and N to be 0.01% or less.
[0088] <Grain Size of Ni-Base Alloy Powder for Additive
Manufacturing>
[0089] The Ni-base alloy powder for an additive manufactured object
according to the embodiment of the invention is made of the Ni-base
alloy having the above-described composition, and an average grain
size thereof is 100 .mu.m or less. In a case where the average
grain size is greater than 100 .mu.m, it is difficult to lay the
powder uniformly during additive manufacturing, and at the same
time, the powder is not sufficiently melted. Accordingly, there is
a concern that pores or joining defects such as non-deposition may
be caused. The lower limit of the average grain size is not
particularly defined, but preferably about 5 .mu.m or greater in
consideration of productivity of powder manufacturing and the like.
In general, an average grain size of the Ni-base alloy powder for
additive manufacturing is within a range of 10 to 45 .mu.m.
[0090] <Heat Treatment Method and Method for Manufacturing
Additive Manufactured Body>
[0091] FIG. 5 shows a flow of a method for manufacturing an
additive manufactured body according to an embodiment of the
invention. A flow of a heat treatment method according to an
embodiment of the invention is included in the flow of the method
for manufacturing an additive manufactured object shown in FIG.
5.
[0092] In the heat treatment method, a solution heat
treatment-aging heat treatment is performed after additive
manufacturing in order to precipitate a .gamma.' phase which
contributes to strengthening of the matrix, as in a general heat
treatment method for a cast material of a Ni-base alloy member. In
this embodiment, it is important to perform a heat treatment for
carbide precipitation optimization under appropriate conditions
before the solution heat treatment-aging heat treatment, that is,
after optionally performing a heat treatment for stress removal on
a shaped object obtained by additive manufacturing. That is, it is
important for MC carbides precipitating due to rapid solidification
during additive manufacturing to be decomposed and
solid-solubilized by a heat treatment for carbide precipitation
optimization, for a .gamma.' phase to be precipitated in a
subsequent aging heat treatment, and for M.sub.23C.sub.6 carbides
to be sufficiently precipitated at grain boundaries.
[0093] In the heat treatment for carbide precipitation
optimization, the heating temperature is equal to or higher than a
temperature T1 determined by Formula (1) according to the
composition of the Ni-base alloy.
[0094] That is, in a case where the temperature is lower than a
certain temperature, MC carbides cannot be decomposed and
solid-solubilized, and the minimum temperature T1 required for this
differs depending on the composition of the Ni-base alloy. The
inventors of the invention have conducted experiments on Ni-base
alloys of various different compositions, and organized the results
thereof by a multiple regression method. They found that in a case
where a heat treatment for carbide precipitation optimization is
performed in a temperature range of the temperature T1 or higher
defined by Formula (1), a material in which M.sub.23C.sub.6
carbides are sufficiently precipitated (a material in which one or
more M.sub.23C.sub.6 carbides are precipitated per 10 .mu.m of
grain boundary length), that is, a material having notch
strengthening characteristics in which the above-described high
temperature creep life ratio is greater than 1, is obtained as the
material after an aging heat treatment.
T1 (.degree. C.)=177.times.Ni (%)+176.times.Co (%)+172.times.Cr
(%)+178.times.Mo (%)+174.times.W (%)+171.times.Al (%)+170.times.Ti
(%)+168.times.Ta (%)+163.times.Nb (%)+307.times.C (%)-16259 (1)
[0095] In Formula (1), the symbol % represents the mass % of each
element. In the component elements described in Formula (1), in a
case where there is a component not contained in the Ni-base alloy
powder to be actually used, it is needless to say that the amount
of the component is 0% in the calculation of Formula (1).
[0096] Hereinafter, the respective steps will be individually
described.
[0097] [Powder Manufacturing Step]
[0098] The powder manufacturing step is a step of manufacturing a
Ni-base alloy powder having an average grain size of 100 .mu.m or
less, which is made of an alloy of the above-described composition.
Although a means for manufacturing the powder is not particularly
limited, for example, a molten alloy of the above-described
composition may be melted in the usual manner, and the molten alloy
may be formed into a powder by, for example, a gas atomization
method or the like. In some cases, sieving may be performed after
manufacturing of the powder to obtain the above-described average
grain size.
[0099] [Additive Manufacturing Step]
[0100] The additive manufacturing step may be performed by a known
method. For example, a Ni-base alloy powder is dispersed on a base
plate (substrate) made of a metal such as SUS316 to form a powder
layer having a predetermined thickness, a region having a
predetermined shape is irradiated with high-density energy such as
a laser or electron beams by a computer program or the like to
rapidly melt the powder in the region, the melt is rapidly
solidified by heat extraction from the base plate side to form a
rapidly solidified layer having a predetermined shape, an alloy
powder is further dispersed on the rapidly solidified layer to form
a second powder layer, the second powder layer in the predetermined
region is melted by high-density energy such as a laser in the same
manner as described above and rapidly solidified to form a second
rapidly solidified layer, and the same process as the formation of
the second rapidly solidified layer is repeated to form an additive
manufactured object having a three-dimensional shape on the base
plate.
[0101] In some cases, a thermal spraying method such as a plasma
spraying method may be applied. In a state in which a Ni-base alloy
powder is melted, droplets of the molten metal may be accumulated
and rapidly solidified in a region having a predetermined shape on
a substrate to form a rapidly solidified layer having a
predetermined shape, a second rapidly solidified layer may be
formed on the rapidly solidified layer by thermal spraying, and the
same process may be repeated to form an additive manufactured
object having a three-dimensional shape on the base plate.
[0102] After the formation of the additive manufactured object on
the base plate, a heat treatment for stress removal of the next
paragraph is optionally performed, and then the additive
manufactured object is peeled off from the base plate by means such
as cutting.
[0103] [Heat Treatment Step for Stress Removal (First Heat
Treatment Step)]
[0104] In the additive manufacturing, residual stress usually
occurs in a shaped object due to local rapid solidification. In
that case, there is a concern that the shaped object may be
deformed due to the residual stress after peeling of the additive
manufactured object from the base plate. In that case, a heat
treatment for stress removal is performed before the peeling. In a
case where the deformation does not matter, the heat treatment is
not necessarily performed. The conditions for the heat treatment
for stress removal are not particularly limited, and in general,
the heating is preferably performed for about 0.5 to 3 hours at a
temperature of 1,000.degree. C. to 1,200.degree. C.
[0105] [Heat Treatment Step for Carbide Precipitation Optimization
(Second Heat Treatment Step)]
[0106] The additive manufactured object optionally subjected to the
heat treatment for stress removal is subjected to a heat treatment
for carbide precipitation optimization. In the heat treatment for
carbide precipitation optimization, the heating is performed for 1
hour or longer and 100 hours or shorter at a temperature not lower
than T1 determined by Formula (1) according to the composition of
the Ni-base alloy and not higher than 1,350.degree. C.
[0107] Through the heating for one hour or longer at a temperature
of T1 or higher, MC carbides can be decomposed, and the carbon (C)
constituting the MC carbides can be solid-solubilized in the
matrix. In a case where the heating temperature is lower than T1 or
the heating time is shorter than 1 hour, separation and
solid-solubilization of the MC carbides are not sufficiently
performed. In a case where the heating temperature is higher than
1,350.degree. C., the additive manufactured object is melted
partially or completely, and thus it becomes difficult to maintain
the shape thereof. In a case where the heating time is longer than
100 hours, the material characteristics are reduced due to the
formation of a surface-altered layer.
[0108] [HIP Treatment Step (Third Heat Treatment Step)]
[0109] A HIP treatment is optionally performed after the heat
treatment for carbide precipitation optimization. The HIP treatment
is performed to eliminate the pores inside the additive
manufactured object by isotropically applying a high pressure at
high temperatures, thereby improving a high-temperature strength,
and in general, the HIP treatment is performed under conditions in
which a pressure of about 50 to 300 MPa is isotropically applied at
1,100.degree. C. to 1,300.degree. C.
[0110] [Solution Heat Treatment (Fourth Heat Treatment Step)]
[0111] A solution heat treatment (solution treatment) is performed
after the HIP treatment is optionally performed. The solution heat
treatment is performed to solid-solubilize the constituent elements
of the .gamma.' phase having an effect of increasing the matrix
strength of the Ni-base alloy, and the heating is performed for 0.5
to 10 hours at a temperature of 1,150.degree. C. to 1250.degree. C.
In a case where the heating temperature is lower than 1,150.degree.
C. or the heating time is shorter than 0.5 hours, the constituent
elements of the .gamma.' phase cannot be sufficiently
solid-solubilized. In a case where the heating temperature is
higher than 1,250.degree. C. or the heating time is longer than 10
hours, there is a concern that the material characteristics may be
reduced due to the formation of a surface-altered layer. Typically,
the heating and holding is preferably performed for 2 hours at
1,200.degree. C.
[0112] [Stabilization Heat Treatment Step (Sixth Heat Treatment
Step)]
[0113] A stabilization heat treatment is optionally performed after
the solution heat treatment. The stabilization heat treatment is a
step of adjusting the form of the .gamma.' phase by
re-precipitating the constituent elements of the .gamma.' phase
solid-solubilized in the solution heat treatment, thereby
exhibiting the strength improving effect by the .gamma.' phase. In
general, the heating and holding are only necessary to be performed
for 0.5 to 10 hours at 950 to 1,150.degree. C. Typically, the
heating is performed for 4 hours at 1,000.degree. C.
[0114] [Aging Heat Treatment Step (Seventh Heat Treatment
Step)]
[0115] An aging heat treatment is performed after the stabilization
heat treatment is optionally performed. The aging heat treatment is
a necessary step for increasing the strength of the matrix by
promoting the precipitation of the .gamma.' phase, and increasing
the grain boundary strength by precipitating M.sub.23C.sub.6
carbides on the grain boundaries, thereby imparting creep notch
strengthening characteristics and improving the high temperature
creep life ratio. In the aging heat treatment, the heating is
performed for 1 to 30 hours at a temperature of 800.degree. C. to
950.degree. C. In a case where the heating temperature is lower
than 800.degree. C. or the heating time is shorter than 1 hour, the
precipitation of the .gamma.' phase and the grain boundary
precipitation of the M.sub.23C.sub.6 carbides do not sufficiently
proceed, and a predetermined aging effect is not obtained. In a
case where the heating temperature is higher than 950.degree. C. or
the heating time is longer than 30 hours, the .gamma.' phase
coarsens, and the strength is reduced.
[0116] In the additive manufactured Ni-base alloy object obtained
by the above method, one or more M.sub.23C.sub.6 carbides are
precipitated on the grain boundaries per 10 .mu.m of grain boundary
length in a metallographic structure of a cross section of the
additive manufactured Ni-base alloy object. Due to the
M.sub.23C.sub.6 carbides, the grain boundaries are strengthened,
and thus the notch strengthening characteristics are exhibited.
Therefore, a high high-temperature creep life ratio can be
exhibited. Accordingly, the additive manufactured Ni-base alloy
object can endure long-term use at high temperatures without being
ruptured early even in a case where it is used as a member such as
a turbine which has a complicated shape and is used at high
temperatures.
[0117] <Application to Turbine Member>
[0118] Basically, the additive manufactured Ni-base alloy object
according to the invention can be suitably applied to all members
requiring a high-temperature strength and creep characteristics,
particularly, a high temperature creep strength. For example, the
additive manufactured Ni-base alloy object according to the
invention can exhibit excellent performance as a turbine member
such as a turbine blade or a member for repairing a turbine
member.
EXAMPLES
[0119] Examples of the invention will be described below together
with comparative examples.
Example 1
[0120] Ni-base alloy powders (grain size: 10 to 45 .mu.m) having
the compositions shown in No. 1 to No. 15 of Table 1 were
manufactured by a gas atomization method. Using the Ni-base alloy
powder, an additive manufactured object was formed on a base plate
made of SUS316 by a metal additive manufacturing apparatus (laser
system, powder bed). Regarding additive manufacturing conditions,
an additive manufactured object was formed such that an average
thickness per solidified layer was 45 .mu.m, 2,300 layers were
laminated, and a maximum thickness was about 100 mm.
[0121] After the additive manufacturing, a heat treatment for
stress removal (1,200.degree. C..times.2 hr) was performed, and the
additive manufactured object was separated from the base plate. For
the shaped objects (invention examples) obtained using the alloys
Nos. 6 to 15, a heat treatment was performed for 2 hours at
1,290.degree. C., that is equal to or higher than T1 of each alloy,
as a heat treatment for carbide precipitation optimization.
Thereafter, the heating was performed for 2 hours at 1,200.degree.
C. as a solution heat treatment, and then the heating was performed
for 4 hours at 1,000.degree. C. as a stabilization heat treatment,
and the heating was further performed for 8 hours at 850.degree. C.
as an aging heat treatment. The shaped objects (comparative
examples) obtained using the alloys Nos. 1 to 5 were not subjected
to the above-described heat treatment for carbide precipitation
optimization, but subjected to the solution heat treatment, the
stabilization heat treatment, and the aging heat treatment under
the same conditions as described above.
[0122] A round bar-like notch test piece (notched test piece) for a
creep rupture test and a smooth test piece were cut out of each
additive manufactured object after the aging heat treatment, and
subjected to a high temperature creep rupture test at 760.degree.
C. according to the high temperature creep test method of JIS Z
2272.
[0123] The overall shape and the dimensions of a notch test piece
(notched test piece) 1 are shown in FIG. 6, and the shape and the
dimensions of a notch part 1B of a parallel part 1A are shown in
FIG. 7. The shape and the dimensions of a smooth test piece 2 are
shown in FIG. 8. Here, a diameter D of the bottom of the notch part
1A of the notch test piece 1 was made equal to a diameter D' of the
parallel part 2A of the smooth test piece 2. The creep test was
performed under uniaxial tensile stress with a load force of 490
MPa.
[0124] Along with the compositions of the alloy powders Nos. 1 to
15, temperatures T1 determined by Formula (1) according to the
compositions are also shown in Table 1. Creep life ratios obtained
by the above-described high temperature creep test at 760.degree.
C., that is, ratios (notch high temperature creep life/smooth high
temperature creep life) of a high temperature creep life (notch
high temperature creep life) determined by the notch test piece to
a high temperature creep life (smooth high temperature creep life)
in a case where the high temperature creep rupture test was
performed on the smooth test piece having no notch, were examined,
and the results thereof are shown in Table 1.
TABLE-US-00001 TABLE 1 Number of M.sub.23C.sub.6 Temperature
Carbides Creep Components (mass %) T1 (per 10 .mu.m of grain Life
No. Ni Co Cr Mo W Al Ti Ta Nb C B Zr (.degree. C.) boundary length)
Ratio Remarks No. 1 Bal. 20.9 19.6 0.4 6.4 0.5 2.1 2.1 1.2 0.14
0.001 0.02 1,264 0.2 0.1 Comparative No. 2 Bal. 18.5 16.6 0.1 7.3
3.2 1.7 1.9 3.2 0.09 0.007 0.02 1,232 0.3 0.2 Examples No. 3 Bal.
17.7 21.8 4.1 7.8 1.2 2.0 1.3 0.5 0.09 0.001 0.01 1,265 0.2 0.1 No.
4 Bal. 20.9 21.2 0.4 0.1 2.8 1.4 2.7 0.1 0.14 0.007 0.04 1,271 0.6
0.3 No. 5 Bal. 17.0 16.9 1.7 5.2 4.6 0.2 0.8 1.4 0.07 0.006 0.00
1,277 0.1 0.1 No. 6 Bal. 21.9 18.1 0.6 5.2 1.6 1.5 2.3 0.3 0.11
0.004 0.01 1,279 3.6 2.7 Invention No. 7 Bal. 17.8 21.1 <0.01
4.9 2.1 1.0 2.0 1.0 0.08 0.003 0.02 1,258 3.2 3.2 Examples No. 8
Bal. 18.2 17.8 1.1 6.4 1.7 2.2 1.2 1.2 0.12 0.004 0.01 1,277 5.2
2.4 No. 9 Bal. 19.1 21.8 1.7 7.6 3.3 <0.01 1.3 <0.01 0.09
0.007 0.04 1,264 5.1 5.1 No. 10 Bal. 18.1 18.5 <0.01 6.1 1.8 3.7
1.3 1.1 0.08 0.007 0.02 1,255 4.3 4.3 No. 11 Bal. 18.7 19.2
<0.01 5.7 1.9 3.5 1.5 1.0 0.06 0.005 0.00 1,254 4.8 4.8 No. 12
Bal. 19.1 15.1 1.8 7.4 2.9 1.2 2.0 0.1 0.13 0.006 0.02 1,292 5.3
2.8 No. 13 Bal. 21.5 15.2 <0.01 5.9 2.1 2.4 2.4 1.4 0.07 0.007
0.00 1,263 3.2 3.2 No. 14 Bal. 18.7 15.8 1.5 7.5 2.6 3.2 0.3 1.5
0.10 0.002 0.00 1,274 2.8 4.4 No. 15 Bal. 18.2 19.8 0.4 4.5 3.1 1.9
<0.01 <0.01 0.15 <0.01 0.04 1,291 3.7 3.7
[0125] In Invention Examples Nos. 6 to 15 subjected to the carbide
precipitation optimization treatment at the temperature T1 or
higher defined in the invention, the creep life ratio is 2 or
greater, and it is obvious that the notch strengthening is
exhibited.
[0126] In Comparative Examples Nos. 1 to 5 not subjected to the
carbide precipitation optimization treatment at the temperature T1
or higher defined in the invention, the creep life ratio is less
than 1, and it is obvious that the notch strengthening is not
exhibited.
Example 2
[0127] The Ni-base alloy powder with the composition of No. 10 in
Table 1 was used and additive manufactured as in Example 1, and the
additive manufactured object obtained was subjected to a heat
treatment for stress removal, a heat treatment for carbide
precipitation optimization, a solution heat treatment, a
stabilization heat treatment, and an aging heat treatment in this
order. The temperature of the heat treatment for carbide
precipitation optimization was variously changed. The conditions
other than the temperature of the heat treatment for carbide
precipitation optimization are the same as in Example 1.
[0128] The additive manufactured object after the aging heat
treatment was subjected to a high temperature creep rupture test at
760.degree. C. as in Example 1 to examine a high temperature creep
life ratio (notch high temperature creep life/smooth high
temperature creep life), and the results thereof are shown in Table
2.
TABLE-US-00002 TABLE 2 Temperature of Heat Treatment for Carbide
Temperature Precipitation Components (mass %) T1 Optimization No.
Ni Co Cr Mo W Al Ti Ta Nb C B Zr (.degree. C.) (.degree. C.) Creep
Life Ratio No. 10 Bal. 18.1 18.5 <0.01 6.1 1.8 3.7 1.3 1.1 0.08
0.007 0.02 1,255 1,200 0.2 1,250 0.3 1,280 3.5 1,290 4.3
[0129] From Table 2, it is seen that in a case where the
temperature of the heat treatment for carbide precipitation
optimization is equal to or higher than the temperature T1
(1,255.degree. C.) of the alloy No. 10, a high creep life ratio is
obtained, and thus notch strengthening is achieved.
[0130] Although the preferable embodiments and examples of the
invention have been described above, these embodiments and examples
are merely examples within the scope of the gist of the invention,
and addition of configurations, omissions, substitutions, and other
changes can be made without departing from the scope of the gist of
the invention. That is, the invention is not limited by the above
description, and is limited only by the appended claims, and it is
needless to say that the invention can be appropriately changed
within the scope.
INDUSTRIAL APPLICABILITY
[0131] According to a heat treatment method for obtaining an
additive manufactured Ni-base object, a method for manufacturing an
additive manufactured Ni-base alloy object, a Ni-base alloy powder
for an additive manufactured object, and an additive manufactured
Ni-base alloy object of the invention, it is possible to improve a
notch high temperature creep life.
REFERENCE SIGNS LIST
[0132] 1: notch test piece [0133] 2: smooth test piece
* * * * *